What happened
On December 2, 2015, a Boeing 787-800 operating at Warsaw Chopin Airport (EPWA) experienced a technical malfunction during taxi operations. After completing the pushback procedure, the aircraft displayed a "BRAKE CONTROLS FAULT" alert, specifically indicating issues with brakes 4 and 8. Due to this system failure, the pilot decided to return the aircraft to its parking stand.
Maintenance efforts were initially focused on replacing the Electric Brake Actuator Control (EBAC R OUTBD) for brake unit number 4. However, this replacement failed to clear the fault. Following consultations with a specialist representative from the brake system provider, the decision was made to replace both brake unit number 4 and brake unit number 8. Following the replacement of the EBAC and brake unit 4, the fault was resolved, and brake unit 8 was also replaced as a precautionary measure per the manufacturer's suggestion.
The investigation
The investigation examined the sequence of maintenance actions and the technical nature of the fault. The investigation established that the manufacturer identified the root cause as a failure within one of the Electric Brake Actuators (EBA). Each brake unit contains four such actuators. The investigation noted that similar previous incidents had occurred where a malfunction in a single EBA caused a failure of the entire EBAC control system.
Findings
- The primary cause of the incident was an internal failure of one Electric Brake Actuator (EBA).
- The failure of a single actuator was sufficient to trigger a fault in the entire EBAC control system.
- Subsequent flight operations of the aircraft showed no further issues with the braking system.